Energy relaxation of resonantly excited polaritons in semiconductor microcavities

Polariton emission has been investigated in a GaAs based microcavity under various excitation conditions which excite predominately hot free excitons and carriers (He–Ne laser excitation), localized excitons (Ti–sapphire laser excitation), or mixed system. Strong differences have been found both in the intensity, the energy distribution, and the temperature dependence of polariton emission for the different excitation conditions. The relaxation into the low polariton branch due to consecutive scattering via polariton states in the bottleneck region and via the states of localized excitons has been found ineffective. Instead, we found that the highly effective filling of low polariton states occurs via relaxation of mobile excitons delocalized due to either thermal activation or interaction with hot carriers.